With development of high speed optical communication technology, people's demands for various services are also growing. For example, the growing demands for information capacity of a single channel in optical communication make the rate of a single wave of the Dense Wavelength-Division Multiplexing (DWDM) system develop from 10 Gbps to 40 Gbps. Currently, the 100 Gbps single wave technology has already appeared and is in constant improvement.
The coherent electric processing method is currently acknowledged as a relatively ideal receiving method for a system with a single-wave rate of 100 Gbps. In the coherent electric processing method, it is necessary to perform a coherent electric processing algorithm after a digital-to-analog conversion, so as to complete demodulation of data information sent by a transmitter. The key point of the coherent electric processing is the correctness of data of an analog-to-digital conversion and a Digital Signal Processing (DSP) algorithm. In order to provide an optimal electric signal data for the DSP algorithm, the information quantity of the analog data sampled by an Analog-to-Digital Converter (ADC) directly determines the demodulation performance of the entire receiving apparatus.
The model of major parts of a coherent receiver disclosed in the prior art is as shown in FIG. 1. Major characteristics of a coherent receiver are as follows. A 90-degree optical frequency mixer is used to perform the coherent frequency mixing of signal lights and local laser lights, where an output wavelength and a power of a local laser are adjusted by a corresponding driver; two quadrature polarization signal lights are output after a signal enters a polarization beam splitter, which are respectively sent to the 90-degree optical frequency mixers together with the beam-split local laser lights at the same time; the optical frequency mixers output four groups of differential signal lights; after the optical-to-electric conversion is performed on each group of differential lights by using a balanced detector, each signal obtained by optical-to-electric conversion goes through a transimpedance amplifier (TIA) for linear amplification of the signal, and finally enters the ADC, which converts analog electric signals into digital signals and sends the digital signals into a subsequent DSP unit for relevant processing and demodulation of information of the signal lights. In the prior art, the disclosed feedback control method has the following principle.
In a feedback control, after modulated signal lights are input into a signal light processor, the frequency mixing of the signal lights and the local laser lights is performed by an adjustable optical coupler; after coupling of the coupler, dual-ended optical signals enter the balanced detector to complete the 0/E conversion; a Radio Frequency (RF) signal processor calculates a feedback quantity for the converted RF signals and outputs the feedback quantity to various executing devices, such as a frequency phase locker, an RF peak detector, and an automatic scanning circuit; and the adjustable optical devices or the local laser is optically adjusted by the executing devices on the circuit. The RF signals through the closed loop control are the received electric signals required after certain kind of processing. In other feedback methods, a feedback of relevant control parameters is given by the DSP unit to adjust the output frequency of the laser, so as to minimize the deviation between the output frequency of the local laser and the frequency of the signal lights.
It can be known that in feedback control in the prior art, devices such as adjustable optical devices and electrical RF processors are used; two kinds of feedback loops, an optical path and a circuit RF signal, work at the same time; only the output RF signals are processed, and accordingly a feedback thereof is given. The DSP unit only feeds back frequency control signals to the local laser.
During the implementation of the disclosed embodiments, the inventors find that the prior art has some defects, for example, the influence of the ADC on the coherent electric processing algorithm is not taken into consideration in the feedback control.